Field of the Invention
This invention relates generally to rotary power transmission systems, and more particularly to tractor transmissions utilizing a fluid coupling with a lock-up clutch.
Tractors employing a transmission that is directly coupled to the engine are difficult to control at low speed. Also, such arrangement requires that the master clutch between range and speed transmissions be slipped when the tractor is moved slowly. Such clutch slipping results in wear and deterioration of the master clutch, and also in a bucking of the tractor. This bucking is not only unpleasant to the operator, but can be quite dangerous in many situations. For example, when a tractor is being hitched to a farm implement or trailer, an unfortunate buck of the tractor might give a discomfitting jolt to a person holding the hitch of the tractor in alignment with the hitch of the implement.
A fluid coupling has a certain amount of slip which reduces the tendency of a tractor to buck and improves low speed control. However, such fluid slip reduces the fuel efficiency of the tractor. Thus, the design of the fluid coupling requires a trade-off between low speed operation and fuel efficiency, with greater slip favoring low speed operation at the expense of fuel efficiency and vice versa. The novel structure and function of elements thereof utilizing a master clutch, speed transmission and high-slip fluid coupling with a lock-up clutch being described hereinbelow represents a significant departure from the prior art.